This invention relates to an unmanned vehicle so constructed that the travel of the vehicle is controlled by a signal from a guidance cable buried near the surface of a travel course.
It has been in practice for the travel control of an unmanned vehicle that an alternating current flows through a guidance cable laid along the travel course. A magnetic field generated by the guidance cable is detected by two pick-up coils provided on the vehicle body, and the steering of the vehicle is controlled according to the difference in the induced voltage between these two pick-up coils. For a stable travelling of the vehicle, a pick-up coil should be installed in front of the rigid wheel with respect to the travel direction. Accordingly, a pair of forward movement pick-up coils and a pair of backward movement pick-up coils are provided, and these pick-up coils are changed as the vehicle travels forwardly or backwardly. When such unmanned vehicle runs forward, the larger the distance between the pick-up coil and the axle of the rigid wheel, the more stable the travel of the vehicle becomes. In the prior art, since this distance is structurally limited, the forward movement pick-up coils are installed with a predetermined angle with respect to the center line of the vehicle body so as to detect an attitude angle. However, by such pick-up coils, only the deflection of a vehicle from the guidance cable or the combined value of the deflection and attitude angle of the vehicle is detected. Moreover, the detected value of the pick-up coils, i.e., the induced voltage, tends to be affected by the variation of the current flowing through the induction cable and inductive disturbances, e.g., change of permeability around the cable, thereby making an accurate travel control difficult.